Interior Secretary James G. Watt, whose revival-style speeches condemning liberals and environmentalists have made him a favorite of ultra-conservatives, will go to work for the conservative Heritage Foundation when he leaves his Cabinet post next month, officials of the group said yesterday.

Watt will work for about four months as a "visiting distinguished fellow in energy and natural resources policy," delivering speeches and writing articles to be distributed to members of Congress, a Heritage spokesman said.

This would not conflict with Watt's reported plans to help with liaison between conservative groups and the Republican Party in 1984, according to Roger Mahan, a spokesman for the foundation.

"He certainly is one of the preeminent people in his field from a conservative standpoint," Mahan said. "This will keep him in a position that will enable him to present his assessment of Interior policies to the Congress and the administration."

Watt could not be reached for comment on his job plans because he was traveling in Tennessee for a series of speeches to conservative Christian groups, including the First Baptist Church of Alcoa, near Knoxville, and the First Assembly of God in Memphis.

He told a cheering congregation of about 300 in Alcoa that he was driven from office not because of his environmental record but because of his "struggle for liberty. That's the real struggle." In Memphis, he said the United States should rely on prayer in handling the crises in Lebanon and Grenada, while opposing "the atheistic forces of communism" seeking to "dominate the world."

The Heritage post would provide Watt with a platform to continue making such speeches, which won him a following on the conservative fund-raising circuit. In 1982, he raised more than $1 million for the GOP through speeches to small gatherings of miners, ranchers, oil and gas company executives and other businessmen. That year, he was the party's No. 1 fund-raiser in the Cabinet.

At Heritage, Watt will be reunited with his former benefactor, Joseph Coors, the conservative brewery magnate who persuaded President Reagan to name Watt interior secretary in 1981. Coors provided the seed money for the creation of the group and is now one of its trustees.

Coors hired Watt in 1977 to run the Mountain States Legal Foundation, a law firm created by Coors to represent miners, ranchers and other western development interests. Before that, Watt was vice chairman of the Federal Power Commission, now the Federal Energy Regulatory Commission.

Watt will the be the latest of several departed Reagan administration appointees to work for the Heritage Foundation. Former national security affairs adviser Richard V. Allen is a "distinguished scholar" for Heritage, former Treasury undersecretary Norman B. Ture worked briefly as a visiting fellow, former Council of Economic Advisers member Steve Hanke is a senior fellow and former National Security Council staffer Richard Pipes is an adjunct scholar.

Watt's first speeches as interior secretary focused on environmentalists, but he soon broadened his attack to liberals and Democrats, portraying them as the "enemies of freedom" who sought to centralize power in Washington.

The real battleground is not the environment, but "what type of government America will have for the generations to come," he said yesterday in Alcoa. " . . . A government that builds up the institutions of power and control to dictate the social behavior and conduct of people? Or will it be a government that lifts up the dignity of the individual and allows that individual to have freedom and liberty?"